This invention relates to a process of purifying wastewater and more in particular to a method of removing metals, colorants, detergents, phenols and the like therefrom.
Normal domestic wastewater is conventionally purified with oxidative biological methods, e.g. in oxidation beds, continuous filters, active sludge plants oxidation ditches or biodiscs. Such methods employ micro-organisms which under aerobic conditions are capable of decomposing and removing organic substances from the wastewater.
In the case of an industrial wastewater, such oxidative biological methods cannot be used sometimes because the micro-organisms are sensitive to various components of the wastewater and the process might be inhibited by the presence or a high concentration of such components therein. Therefore, chemical and/or physical purification methods such as precipitation of metals in hydroxide or sulfide form, adsorption of metals to ion exchangers, adsorption of colorants to active carbon, removal of detergents by flocculation, or extraction of phenols with an organic solvent, whether or not in combination with a biological purification process, are frequently used in the case of industrial wastewater. While such methods are generally satisfactory, there is always a need for other methods capable of removing such components from wastewater with high efficiency.
Document EP-A-0 110 240 discloses a method of removing heavy metals from wastewater. This method employs surplus sludge from a normal aerobic biological water purification process which has been subjected to an anaerobic fermentation for some time. The sludge is contacted with the wastewater under anaerobic conditions and appears to be capable of adsorbing heavy metals from the wastewater. After completion of a certain contact period, the sludge together with the heavy metals adsorbed thereon is separated from the wastewater and the remaining wastewater may be discarded or supplied to a normal oxidative biological water purification process.
However, a disadvantage of the method of EP-A-10 110 240 is that the contact period must be a rather long period (up to 24 hours) if it is desired to have a sufficient adsorption of heavy metals from the wastewater. Moreover, the adsorption is effected under anaerobic conditions, and this means that structural provisions must be made to seal the adsorption space from the outside in an airtight way.
An object of the invention is to remove the disadvantages of the method disclosed in EP-A-0 110 240 and to provide a water purification method capable of adsorbing metals from wastewater in a rapid and efficient way, without airtight sealing. Another object is to provide a method permitting an efficient adsorption of colorants, detergents, phenols, and the like from wastewater.